1. The Field of the Invention
The present invention relates to foam sensor systems used in reactors, such as bioreactors and fermenters, for controlling foam levels within the reactor bags so as to prevent unintentional clogging of the gas exhaust filters.
2. The Relevant Technology
It is now common in the biopharmaceutical industry to use bioreactors where the portion of the reactor that contacts the culture of cells is disposable so that no sterilization or cleaning is required between different batches. One example of a disposable type reactor includes a large flexible bag that is disposed within a support housing, the bag containing the cell culture that is being grown. A sparger is used to deliver needed gases to the culture while an impeller located within the bag is used to continuously mix the culture. The sparger gas exits out of the bag through a gas exhaust filter.
To help prevent or limit shear damage to the cells caused by the impeller, a surfactant is typically added to the culture. However, the combination of the surfactant, waste product from the cells, and the sparger gas passing through the culture results in the continual production of foam that collects on top of the culture within the reactor bag. If the produced foam is permitted to continue to build up within the reactor bag, the foam will eventually be drawn out of the gas exhaust line with the sparger gas and pass into the gas exhaust filter. Because the foam is very sticky, the foam will almost immediately clog the filter, thereby causing the reactor to shut down because the sparger gas can no longer escape the reactor bag. The scenario is known as “foaming-out.” Once the reactor shuts down, the cells will quickly die and the entire culture will be lost. As a result, the foaming-out of a bioreactor can be extremely expensive due to the loss of the culture, the loss of the previous time and effort used in growing the culture, and the required time and expense to start the process over again with a new reactor bag and culture. In addition, foaming-out can significantly delay production time.
To help prevent foaming-out, an anti-foaming agent can be added to the culture while it is growing within the reactor bag. The effectiveness of the anti-foaming agent, however, is only temporary. As such, the bioreactor must be continually monitored through the production cycle and additional anti-foaming agent added as needed. This process, however, is labor intensive and is prone to failure if the reactor is not closely monitored. To help eliminate the required monitoring, relatively large quantities of anti-foaming agent are often added to the culture at set time intervals, independent of the foam production. This process, however, tends to use more anti-foaming agent than is actually needed to control the foam. Using anti-foaming agents and particularly excessive amounts of anti-foaming agents can be problematic in that the anti-foaming agent can build up on the surfaces that it contacts, which can cause production problems, and because the anti-foaming agent eventually needs to be removed from the culture in a downstream production step. The more anti-foaming agent in the culture, the more difficult and time consuming it is to remove the anti-foaming agent from the culture.
Accordingly, what is needed in the art are reactor systems that limit all or at least some of the above problems.